Through years of development of an existing power inductor, an assembly type inductor slowly tends to be marginalized due to difficulty in realization of automation, while two types can basically realize the automation as follows: the first type is an integrally molded mold-pressing inductor which is made by mixing and granulating metal powder and resin and then performing mold pressing with a coil through a metal mold. Due to extremely high saturated magnetic flux density of the metal powder in the inductor, an excellent direct-current saturation characteristic can be obtained, as shown in FIG. 1(1). The other type of inductor is obtained by adopting an I-shaped ferrite magnetic core, directly winding a coil on the magnetic core and then coating an outer part by adopting magnetic glue to enclose a magnetic circuit. The I-shaped magnetic glue inductor is often called an NR inductor. Since an electrode is directly metalized on the ferrite magnetic core, the inductor is high in drop impact resistance, simple in manufacture procedure and high in degree of automation, as shown in FIG. 1(2). The two inductors are widely applied in various electronic devices such as LED illumination devices, multifunctional mobile phones, flat-panel TVs, blue ray DVDs, set top boxes, laptop computers, desktop computers, servers, display cards, portable devices, multimedia devices, etc.
However, the two inductors respectively have disadvantages through comparison. The former is not high enough in yield and has lower degree of automation than the later due to many production procedures in compression molding and a high pressure of a hydraulic press needed in mass production; and the latter often has poor direct-current saturation characteristic than the former due to the low saturated magnetic flux density of the adopted ferrite magnetic core, and since a magnetic permeability of the magnetic glue coated on the outer part is generally low, a direct-current resistance relative to the mold-pressing inductor is high.